Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$138.88	12.114%	$155.7039	$155.70	$155.70	$155.70
Purchase #2	$223.69	10.316%	$246.7659	$246.77	$246.75	$246.80
Purchase #3	$100.81	10.430%	$111.3245	$111.32	$111.30	$111.30
Purchase #4	$53.29	6.376%	$56.6878	$56.69	$56.70	$56.70
Purchase #5	$221.31	4.391%	$231.0277	$231.03	$231.05	$231.00
Purchase #6	$20.84	6.848%	$22.2671	$22.27	$22.25	$22.30
Purchase #7	$90.39	11.361%	$100.6592	$100.66	$100.65	$100.70
7 purchase totals =	$849.21		$924.4361	$924.44	$924.40	$924.50